Transdifferentiation or induction occurs when cells of one phenotype are transformed, in the presence of one or more growth and differentiation factors, into cells of another phenotype. One example is the response of connective tissue to demineralized bone powder. In the presence of demineralized bone powder, connective tissue cells are converted to chondroblasts, and produce a cartilage matrix that is resorbed and replaced by bone.
Devices used for the study of transdifferentiation have often relied upon semipermeable membranes as a support for the required growth and differentiation factor(s) and for the cells that are acted upon by these factors. These semipermeable membranes often induce an inflammatory response in a subject when implanted in vivo. Moreover, in vivo assays designed to test the ability of growth and differentiation factors, and other molecules that modulate this activity, are often expensive, cumbersome, and time-consuming. Furthermore, prior culture devices have suffered from problems associated with dispersion of growth and differentiation factors on the surface of a support. The factors are ineffective because the levels in the support are too low to cause the desired effect. As a result, in vitro systems for promoting transdifferentiation and and in vivo implants designed to induce transdifferention have been generally ineffective.